RU2122982C1 - Drinking water production process - Google Patents

Abstract

FIELD: drinking water production. SUBSTANCE: invention relates to treatment of water, industrial and household waste waters with special emphasis on multistage water treatment and as well to producing drinking water by treating natural surface and underground waters. Invention aims at reducing secondary pollution of water by toxic products formed upon treatment of natural water containing organic compounds. Production of drinking water consists in treating original water with ozone (oxidant) followed by reagent processing in forced flotation manner with coagulant as flotator, reozonation, filtration through activated carbon, and disinfection with chlorine as oxidant. Ozone/ozone/chlorine ratio is 1:(1-4):(0.3-1.0). EFFECT: increased quality of drinking water (4-8- fold reduction of toxic product level). 2 cl, 2 tbl

Description

 The invention relates to the field of water treatment, industrial and domestic wastewater, in particular to multi-stage water treatment, and can be used for the preparation of drinking water by treating natural, surface and groundwater.

 Numerous technological schemes for the preparation of drinking water are known, based on the processes of oxidation, coagulation, and filtering with their various combinations depending on the composition of the source natural water.

So, there is a known method of producing drinking water using the processes of coagulation, sedimentation, chlorination, filtering and ozonation [F.A. Shevlev, G.A. Orlov. Water supply of large cities of foreign countries. - M .: Stroyizdat, 1987 .-- 351 p., P. 24 - 28]. The source water enters the mixing chamber, where it is treated with a coagulant-solution of aluminum sulfate at the rate of 10 - 20 mg / dm ³ , and is sent to sedimentation tanks, the average residence time of water in which is about 7 days. Before the last sump, a solution of aluminum sulfate in a dose of 10 - 20 mg / dm ³ is re-introduced into the water, then the water enters the mesh drum filters and is chlorinated in doses of 5 - 10 mg / dm ³ , followed by treatment with aluminum sulfate (a third time) and activated silicic acid. Doses of reagents are respectively 10 - 20 and 0.5 - 3.0 mg / DM ³ . After passing fast filters, consisting of quartz sand with a grain size of 0.4 - 0.8 mm, a layer thickness of 300 mm and anthracite with a grain size of 0.8 - 1.4 mm, a layer thickness of 600 mm, when the filtering speed reaches 10 m / h , the filtrate is treated with ozone and sent to a clean water tank. Before feeding into the network, the filtrate is disinfected with chlorine (about 0.5 mg / dm ³ ).

The method described above (flow chart, techniques, operations) was used to prepare drinking water from natural water - the Dnieper River. Dnieper water is characterized by a high content of organic substances, mainly humic compounds. Our studies have shown that the chlorination of water (7 mg / dm ³ ) before the third coagulant treatment with an initial color of 53 ^o , a turbidity of 4.4 mg / dm ³ and a content of 106.3 mg / dm ^{3 of the} sum of humic compounds and fulvic acids (G + F ) 15 mg / dm ^{3 the} sum of aldehydes and ketones (A + K), COD = 36 mgO ₂ / dm ³ and <2 mg / dm ³ chloroform (hereinafter composition 1) leads to the formation of toxic organochlorine compounds (ChOS) - chloroform, which practically cannot be removed at subsequent stages of water treatment and enter the treated water. The concentration of chloroform in the resulting drinking water is 197 mg / dm ³ , which is 3.3 times higher than the maximum permissible concentration of 60 μg / dm ³ [N.G. Rybalsky, O.L. Jackets and others. Environmental aspects of the examination of inventions. Handbook of expert and inventor. Part 1. - M .: VNIIIPI, 1989 .-- 448 p., P. 121].

 It should be noted that the water of the river. The Dnieper also contains a fairly large number of phyto- and zooplankton and microorganisms, which require a long time and large volumes of structures to remove in traditional coagulation and sedimentation processes, which in turn requires large areas.

 The disadvantages of this method are the secondary pollution of the resulting drinking water with organochlorine compounds, a decrease in the efficiency of purification from the starting organic compounds, the duration of the water purification process.

 A known method of preparing drinking water, which consists in prechlorination of river water, reagent treatment, filtration of clarified water, treatment of the filtrate with ozone, followed by sorption on granular carbon filters [Level and indicators of the development of housing and communal services of foreign countries: Scientific works of the Academy of Public Utilities named after K.D. Panfilova / ONTI A.K.K. - M., 1975, no. 114, p. 35 - 38]. Prechlorination of water is carried out at a dose corresponding to the point of fracture. Then the water is fed to mixers with mechanical mixers, where the batchers introduce solutions of aluminum sulfate and activated silicic acid. After the reagent treatment, water enters the clarifiers with suspended sediment of the "Pulsator" type. The clarified water is directed to quick filters loaded with quartz sand with a layer of 800 mm and a grain size of 0.95 mm. Filtering speed on sand filters reaches 9 m / h. After the filtrate is treated with ozone, water is directed to the quick filters loaded with granular activated carbon with a layer of 1300 mm and a grain size of 0.63 mm, and then it enters the clean water tank.

The use of this technological scheme for obtaining drinking water from the Dnieper showed the following. In the process of river water prechlorination, organochlorine products are formed that are ineffectively removed during subsequent coagulation, and ozonation of chlorinated water exacerbates repeated water pollution due to the formation of toxic organic substances that are more dangerous to human health than the starting substances. So, drinking water obtained from the river. The Dnieper (composition 1) contains HOS-chloroform in an amount of 235 μg / dm ³ , which is 4 times higher than the MPC, which is the main disadvantage of the method that prevents the use of natural water with a high content of organic pollutants for drinking water.

Closest to the invention in terms of technical essence and the achieved effect is a known method for producing drinking water, in which river water is treated with ozone and fed to a bulk reservoir. The duration of water in it is 3-4 days. Water is supplied from the reservoir to mixers with mechanical mixers, where coagulant-aluminum oxychloride and chlorine dioxide are introduced for preliminary chlorination. The dose of chlorine dioxide does not exceed 4.7 mg / DM ³ . Further, the water passes through the flocculation chambers equipped with mechanical mixers, multi-tier sedimentation tanks and quick sand filters. The filtering speed is 9 m / h, the thickness of the loading layer is 1.4 m with an average grain size of sand 1 mm. The filtrate is re-treated with ozone and fed to sorption filters loaded with activated carbon. The filtering speed is 9 m / h, the thickness of the loading layer is 1 m with an average particle size of coal particles of 1 mm. After carbon filters, ozone is introduced into the water for the third time. The average dose of ozone is 3.8 mg / dm ³ , including 0.8 mg / dm ³ for preliminary ozonation. For the final (third) ozonation, the dose of ozone is determined on the basis of ensuring residual ozone at the level of 0.4 mg / dm ³ for 4 minutes. The final process of water treatment is its chlorination with small doses of sodium hypochlorite before supplying clean water to the tanks.

 As follows from the technical essence, the known method involves triple ozonation, prechlorination and disinfection of chlorine in the process of preparing drinking water. However, it is known that the combination of ozonation and chlorination of river water is contraindicated due to a significant increase in the content of organochlorine compounds in drinking water [Alekseeva L.P. The effect of a combination of ozonation and chlorination of water on the formation of chloroform // Chemistry and Technology of Water. - 1986. - 8, N 5, p. 62 - 64], which is confirmed by our data.

So, in the preparation of drinking water from the water of the river. The Dnieper, which contains natural organic compounds (humic and fulvic acids), using the known method, chlorination of ozone-treated water and aged for a long time leads to the formation of a large number of toxic organochlorine compounds that are practically not removed at the subsequent processing stages (coagulation, sedimentation filtering through sand filters). Repeated ozonation of the filtrate leads to a further significant increase in the concentration of toxic products, i.e. a combination of ozonation-chlorination-ozonation processes during the treatment of the Dnieper water (composition 1) leads to secondary pollution of purified water with toxic substances, and in quantities significantly exceeding the MPC: the chloroform content in purified water is 163 μg / dm ³ .

In addition, the process of obtaining drinking water from the river. According to the known method, the Dnieper is characterized by a rather long duration, mainly due to processes, coagulation, sedimentation (3.5 hours), and with a large station capacity (> 120,000 m ³ / day), voluminous structures occupying large areas will be required.

 Thus, from the prior art it follows that the known methods for the preparation of drinking water do not solve the problem of improving the quality of water by eliminating the secondary pollution of water formed by the treatment of toxic products with oxidizing agents.

 The objective of the invention is to develop such a method for producing drinking water by treating natural water with ozone in several stages in combination with physicochemical processes, in which changing the conditions of the reagent treatment and treatment with an oxidizing agent would improve the quality of drinking water by reducing the secondary pollution of water with toxic products formed in the process of purification of natural water containing organic compounds, as well as a significant reduction in the duration of the process of obtaining drinking water due to the acceleration of coagulation and sedimentation processes.

To solve this problem, a method for producing drinking water is proposed, including treating the source water with an oxidizing agent - ozone followed by reagent treatment, re-treating the oxidizing agent with ozone, filtering through activated carbon and disinfecting the purified water with an oxidizing agent - chlorine, in which according to the invention the reactant treatment is carried out in pressure mode flotation, and a coagulant is used as flotation reagent, and the dose of oxidizing agent at each stage is selected from the ratio ozone: ozone: chlorine equal to 1: (1-4) :( 0.3-1.0), p In this case, a flotation reagent of concentration 40-60 mg / dm ^{3 is used} .

 We have found that the claimed dose ratio of ozone: ozone: chlorine are selected from conditions that ensure deep purification of water from organic substances and disinfection, preventing re-contamination of purified water with organochlorine compounds.

The claimed dose ratio of ozone is optimal:
- to ensure the necessary depth of oxidation of natural organic compounds (humic acids) to carboxylic compounds, which are effectively removed during subsequent coagulation. So, for example, carboxylic acids formed as an oxidation product enter into complexation with aluminum ions (coagulant) and form insoluble compounds, which are centers of further crystallization, which contributes to a deeper course of the coagulation process;
- to prepare the remaining amount of organic compounds contained in water for effective biodegradation in the loading of activated carbon.

 The final chlorination of purified water at the claimed ratio with doses of ozone avoids the formation of organochlorine compounds and provides the necessary degree of disinfection of water.

 It should be emphasized that deep water purification from organic and suspended substances, hydrobionts and algae is achieved by combining the claimed ozone treatment regimes with reagent treatment under pressure flotation using a coagulant as a flotation reagent. This nature of the reagent treatment allows you to abandon the prechlorination of raw river water and use only ozonation. Due to the intensification of coagulation processes in the flotation treatment mode, the processing time is reduced from 3-4 hours when using traditional technology of coagulation water treatment to 20-30 minutes.

 It is very important that in the process of flotation coagulation, the blue-green algae are effectively removed, which easily float and are removed. This prevents decay processes in stagnant zones and biological fouling of treatment facilities.

 The result of the proposed integrated technological scheme for the preparation of drinking water is also a reduction in the volume of structures occupied by land, a reduction in investment.

 Thus, the claimed combination of essential features of a method for producing drinking water is new and necessary to achieve the technical result provided by the invention — prevention of re-contamination of water with toxic compounds formed during the processing of the source water, which provides a significant increase in the quality of drinking water, as well as a reduction in the duration of the process obtaining high-quality drinking water while reducing the volume of structures and occupied space.

 The method is implemented as follows.

To obtain drinking water, natural water of the river is treated. Dnieper containing 106.3 mg / dm ³ sums of humic compounds and fulvic acids (G + F), 15.0 mg / dm ³ amounts of aldehydes and ketones (A + K), <2 mg / dm ³ chloroform, COD = 36 mgO ₂ / dm ³ .

Water is treated in the following sequence of technological operations. Water in an amount of 15 dm ^{3 is} placed in a contact tank, which is a hollow column with a bubbler in the lower part, and is subjected to ozonation with a dose of ozone of 3.3 mg / dm ³ for 7 min. Ozone is obtained on a laboratory ozonizer with a capacity of 10 g / h produced by the OP SKTB Institute.

Then, ozonated water is subjected to reagent treatment in pressure flotation mode by directing water sequentially into a mixer with mechanical mixers, a flocculation chamber and a flotation column. 0.75 dm ³ of a coagulant-aluminum sulfate solution with an initial mass concentration of 10 mg / dm ³ is introduced into the mixer. Mixing water with a coagulant is carried out at a speed of 60 rpm for 5 minutes The water treated with the coagulant enters the flocculation chamber, where it remains for 10 minutes. From the chamber, water is sent to a flotation column, where recirculation (tap) water is introduced in a proportion 1: 4 to the volume of water to be purified, pre-saturated with air in a saturator (pressure vessel), through a throttling device; 3.8 dm ³ . The flotation time equal to the time of clarification of the liquid due to the removal of coagulated suspension into the foam layer is 10 minutes.

The clarified water enters the sand filter loaded with quartz sand with a layer of 800 mm and a grain size of 0.95 mm, the filtration speed is 7 m / h, the filtrate is sent to a contact tank for ozonation of water at an ozone dose of 3.30 mg / dm ³ for 10 min . The ozone-treated water enters the sorption filters loaded with granular activated carbon. The filtering speed is 6 m / h with a loading height of 2 m and an average particle size of coal particles of 1.5 - 2.0 mm.

The water purified on carbon filters is subjected to chlorine disinfection with a dose of 1.0 mg / dm ³ for 40 minutes. The ratio of oxidizing agents O ₃ : O ₃ : Cl ₂ is 1: 1: 0.3. The obtained drinking water is characterized by the following indicators (table. 1, example 4): COD = 17.0 mgO ₂ / dm ³ , (G + F) = 31.3 mg / dm ³ , color 6 ^o , turbidity 0.14 mg / dm ³ , (A + K) = 13 mg / dm ³ , chloroform 26.5 μg / dm ³ , aluminum 0.08 mg / dm ³ . Such indicators indicate a high quality of drinking water, while some of them exceed the requirements of GOST and MPC.

So, according to GOST "Drinking water" 3351-74, the color is 20 ^o , and the turbidity of 1.5 mg / DM ³ (in the example of 6 ^o and 0.14 mg / DM ³ respectively).

According to the requirement of the WHO Guidelines for Drinking Water Quality Control 1977 - 1978, the residual concentration of aluminum should not exceed 0.2 mg / dm ³ (in the example, 0.08 mg / dm ³ ); and, as mentioned earlier, according to the requirement given The maximum concentration limit for chloroform is 60 μg / dm ³ (in the example 26.5 μg / dm ³ ), it should be emphasized that the quality of drinking water obtained according to the described example significantly exceeds the quality of drinking water obtained by a known method, primarily secondary pollution indicators: chloroform content reached AET 163 g / dm ^3, which is 6 times that of Example.

 When implementing the inventive reagent treatment regimen, the time of coagulation and removal of coagulated and swallowed contaminants, including zooplankton and phytoplankton, is 30 min, which is 7 times less than by the known method.

 Similarly to the example implementation of the method, experiments were carried out to obtain drinking water from the water of the river. The Dnieper of composition 1, when treated with oxidizing agents both in the claimed range of ratios and beyond, using coagulants of various nature as flotation reagents in amounts that are in the claimed dose range and beyond. The data are presented in table 1.

As a coagulant, aluminum sulfate is used - Al ₂ (SO ₄ ) ₃ (GOST 3758-75), industrial alumina - TG containing 51.3 - 58.12% Al ₂ (SO ₄ ) ₃ (GOST 12966-85), hydroxyl chloride aluminum - (passport N 31) containing Al ₂ (OH) ₅ Cl 9.1%.

 It has been established that the claimed ratio of oxidizing agents ozone: ozone: chlorine, carrying out reagent water treatment in pressure flotation mode using a coagulant as a flotation reagent, and the claimed doses of flotation reagent are selected from conditions that provide the necessary depth of oxidation of organic contaminants to compounds that are effectively removed in the coagulation processes, flotation and filtering, as well as the almost complete prevention of the formation of ChOS in the treated water with a minimum content of residual aluminum (table 1, examples 1 - 14).

The oxidation process at a prohibitive ratio of O ₃ : O ₃ = 1: 4,5, i.e. with an increased dose of ozone in the second stage, it leads to a decrease in the degree of purification from the starting organic compounds (concentration (G + F) reaches 41.2 mg / dm ³ ), as well as to secondary pollution of drinking water - concentration (A + K) reaches 34 5 mg / dm ³ , and chloroform 42.3 μg / dm ³ , which exceeds their content in the source water by 3 and 21 times, respectively (table 1, example 15).

The prohibitive ratio of O ₃ : O ₃ = 1: 0.50, which corresponds to the conditions for oxidation at a reduced dose of ozone in the second stage, leads to a sharp decrease in the effect of purification from organic substances - the concentration (G + F) reaches 73.7 mg / dm ³ , COD - 31 mgO ₂ / dm ³ . The indicators of purified water are lower than those of the prototype (table 1, examples 16 and 21).

Reducing the dose of chlorine during the disinfection process (O ₃ : O ₃ : Cl ₂ = 1: 2: 0.2) leads to the absence of residual chlorine after 30 minutes of contact with water, and therefore, the bacterial safety of the water in the distribution network is not ensured; secondary bacterial contamination of drinking water, which is unacceptable (table 1, example 17).

When using an increased dose of chlorine in the disinfection process (O ₃ : O ₃ : Cl ₂ = 1: 2: 1,2 ratio), secondary pollution of drinking water occurs - the content (A + K) reaches 55 mg / dm ³ , and chloroform - 65 μg / DM ³ (exceeds the MAC) (table 1, example 18).

It has been experimentally established that the optimal dose of flotation agent - coagulant is 40-60 mg / dm ³ . The specified dose provides an effective removal of coagulated and swallowed organic pollutants, phyto- and zooplankton with a minimum content of residual aluminum in the water.

When the coagulant dose is both lower than the claimed limit and higher, a decrease in the effect of water purification is observed, which is especially pronounced with an exorbitant dose reduction (color reaches 22 ^o , turbidity - 1.65 mg / dm ³ ). In both cases, secondary contamination of drinking water with aluminum occurs, the content of which increases to 0.52 - 0.57 mg / dm ³ (table 1, examples 19 and 20).

Provided by the proposed method, the high quality of drinking water is also confirmed by the data of table 2, which reflects the achieved result when treating water of the river. Dnieper, characterized by different color, turbidity, COD, the content of humic substances. When using water with high turbidity (compositions 2 and 3), it is advisable to add a small amount (0.05 mg / dm ³ ) of flocculant during reagent treatment. Magnoclocks of the American company Watertec. Inc. can be used as flocculants, for example, MF-1906 N-high molecular weight non-ionic highly active; MF-573 s - low molecular weight cation exchanger; MF-835A is a high molecular weight anion exchange resin.

The advantages of the proposed method for producing drinking water are shown in tables 1,2. As follows from the data presented, the proposed method provides, in comparison with the known improvement in the quality of drinking water obtained, which is expressed primarily in the prevention of secondary pollution with toxic organochlorine compounds - the chloroform content is 21.1 - 37.5 μg / dm ³ , which is ≈ 1.6 - 3 times lower than the MPC, while the use of known technology leads to a chloroform content of 163.0 μg / dm ³ , which is 2.7 times higher than the MPC. Thus, secondary pollution of CWD is reduced by 4-8 times.

The cleaning effect of primary organic compounds also increases - the content (G + F) is 25.1 - 34.5 mg / dm ³ , which is 1.75 - 1.25 times lower than in drinking water obtained by the known method. Moreover, the proposed method reduces the duration of the process of obtaining drinking water by accelerating the coagulation and sedimentation processes from 3 to 4 hours to 20 to 30 minutes, i.e. 6 to 9 times in comparison with the known method.

It should be noted that the residual concentration of aluminum in drinking water is at the level of 0.2 mg / dm ³ and lower, which confirms the high quality of the resulting water.

Claims (2)

 1. A method of producing drinking water, comprising treating the source water with an oxidizing agent - ozone, followed by reagent treatment, re-treating with an oxidizing agent - ozone, filtering through activated carbon and disinfecting the purified water with an oxidizing agent - chlorine, characterized in that the reactant treatment is carried out in pressure flotation mode, and a coagulant is used as a flotation reagent, and the dose of oxidizing agent at each stage is selected from the ratio of ozone: ozone: chlorine equal to 1: (1 - 4): (0.3 - 1.0). 2. The method according to claim 1, characterized in that the dose of flotation reagent is 40-60 mg / DM ³ .

Images